1. Field of the Invention
The present invention relates to an ultrasonic diagnostic apparatus equipped with a probe unit including an oscillation body operable to control the aperture of transmission and reception of the ultrasonic waves to be emitted to and reflected by the object being observed.
2. Description of the Related Art
Conventionally, there have been provided an ultrasonic diagnostic apparatus designed to control the aperture of the ultrasound beam. The ultrasonic diagnostic apparatus of this type is disclosed in Japanese Patent Laying-open Publication No. 7-107595 and shown in FIG. 10. This apparatus comprises a piezoelectric layer 91, an acoustic matching layer 92, and a backing block 93 supporting the layers 91 and 92. The piezoelectric layer 91 is divided into a plurality of segments arranged in the azimuthal direction Da of the probe unit. The thickness of the piezoelectric layer 91 in the minor axis direction Dm is small in the center of the piezoelectric layer 91 but large at each end of the piezoelectric layer 91. The probe unit of the ultrasonic diagnostic apparatus is therefore capable of obtaining a broadband frequency characteristic because of the fact that the center portion of each segment mainly senses high frequency ultrasonic waves while the end portion of each segment mainly senses relatively low frequency ultrasonic waves. The aperture of the piezoelectric layer 91 of the probe unit, i.e., the aperture for transmitting and receiving the ultrasonic waves is controlled by the signal transmitting unit 95 and the signal receiving unit 96 in inverse proportion to the frequency of the ultrasonic waves passing through the piezoelectric layer 91. This results in the fact that the image resolution of the ultrasonic diagnostic apparatus is improved at any focal distance of the ultrasonic diagnostic apparatus.
The conventional ultrasonic diagnostic apparatus thus constructed in the above, however, encounters such a problem that the piezoelectric layers are required respectively to be machined in the shape of a plano-concave element and to be precisely laminated in their adhesive processes.
The present invention contemplates resolution of such problems.
It is therefore an object of the present invention to provide an ultrasonic diagnostic apparatus with a readily machinable oscillation body without declining the resolution of the ultrasonic diagnostic apparatus at any focal distance and to facilitate the machining and adhesive processes of the oscillation body.
According to one aspect of the present invention, there is provided an ultrasonic diagnostic apparatus for observing a detectable object to be ultrasonically diagnosed, comprising: an ultrasonically diagnostic probe unit for probing the detectable object with the ultrasonic waves emitted to the detectable object in response to input pulse signals and with the ultrasonic echo from the detectable object; a signal transmitting unit operatively connected with the ultrasonic diagnostic probe unit to generate the input pulse signals to be transmitted into the ultrasonic waves by the ultrasonically diagnostic probe unit; a signal receiving unit operatively connected with the ultrasonically diagnostic probe unit for receiving the ultrasonic echo from the detectable object and processing output signals to be converted into the image of the detectable object being observed; a display unit operatively connected with the signal receiving unit to display the image of the detectable object on the basis of the output signals from the signal receiving unit to ensure the ultrasonically diagnosed state of the detectable object. The ultrasonically diagnostic probe unit comprises an oscillation body having a pair of piezoelectric layers, an intermediate layer sandwiched by the piezoelectric layers, an acoustic lens body operative to focus the ultrasonic waves to be emitted to and reflected by the detectable object, and a supporting body having the oscillation body mounted thereon to ensure that the detectable object is probed by the oscillation body to be ultrasonically diagnosed with the display unit.
The signal receiving unit may have a wave propagation direction along which the ultrasonic waves propagate, an azimuthal direction perpendicular to the wave propagation direction, and a minor axis direction perpendicular to the wave propagation direction and the azimuthal direction, and one of the piezoelectric layers of the oscillation body may have a central portion extending along the azimuthal direction and a pair of end portions integrally formed with the central portion. In this case, the total thickness of the end portions of the piezoelectric layers is smaller than that of the central portion of the piezoelectric layer, and the thickness of each end portion of the intermediate layer is larger than that of the central portion of the intermediate layer.
In the above ultrasonic diagnostic apparatus, the piezoelectric layers of the oscillation body may have respective cross sections taken on the plane parallel to the wave propagation direction and the azimuthal direction and each including a truncated convex portion and a rectangular portion integrally formed with the truncated convex portion, the truncated convex portion having a bulged contour constituted by a flat center surface portion and a pair of inclined surface portions having the center surface portion positioned therebetween in the minor axis direction and each inclined to have its first end connected to the center surface portion and its second end connected to the cross sectional contour of the rectangular portion. In this case, the center surface portions of the piezoelectric layers are held in buttjoint engagement with each other and the intermediate layer has a pair of wedge portions opposed to each other and outwardly gradually thickening as the corresponding two positions of the wedge portions space apart from each other.
The truncated convex portions of the piezoelectric layers may be held in contact with each other at the flat center surface portions of the truncated convex portions.
The piezoelectric layers may respectively have first side surface portions formed with a plurality of grooves and second side surface portions opposed to each other, and the first side surface portions may be segmented into a plurality of element regions with the grooves spaced apart from one another in the azimuthal direction.
In the case that the oscillation body has three directions consisting of a wave propagation direction, an azimuthal direction and a minor axis direction and that the intermediate layer of the oscillation body has a central portion extending along the azimuthal direction and a pair of end portions and integrally formed with the central portion, the thickness of the end portion of the intermediate layer may be mechanically equal to that of the central portion of the intermediate layer under the condition that the central portion of the intermediate layer has predetermined acoustic impedance ultrasonically different from that of each end portion of the intermediate layer.
In this case, the intermediate layer of the oscillation body may have different material portions different in acoustic impedance and adjacent to one another. The different material portions preferably include a high impedance portion having predetermined acoustic impedance and a pair of low impedance portions having respective acoustic impedance lower than that of the high impedance portion. Further, the intermediate layer of the oscillation body may have a pair of intermediate impedance portions each having acoustic impedance lower than that of the high impedance portion and higher than that of the low impedance portion. In this case, the intermediate impedance portions are provided preferably between the high impedance portion and the low impedance portion in the minor axis direction.
It is preferable that the piezoelectric layers of the oscillation body be made of a ceramic material and that the intermediate layer of the oscillation body have acoustic impedance of 2 through 8 Mrayl. The intermediate layer may be made of a resin.
It is also preferable that the oscillation body further include an acoustic matching layer provided between the acoustic lens body and the piezoelectric layer facing to the acoustic lens body. In this case, the matching layer preferably serves as the quarter wave plate.
The acoustic lens may have a first lens portion of a short focal distance and a second lens portion of the focal distance longer than that of the first lens portion, the second lens portion having the first lens portion positioned therein.
The ultrasonic diagnostic apparatus according to the present invention may further comprise: a first lead member electrically connected to the interior surfaces of the truncated convex portions of the piezoelectric layers; and a second lead member electrically connected to both of the exterior surfaces of the piezoelectric layers, and one of the first and second lead members is connectable to the ground and the other of the first and second lead members being connectable to the signal transmitting unit and signal receiving unit.
The signal transmitting unit may be operative to generate the input pulse signals as the impulse signals or the chirp pulse signals to be transmitted into the ultrasonic waves by the ultrasonically diagnostic probe unit.
The signal receiving unit may have a dynamic filter having the output signals pass therethrough and changed from a high frequency range to a relatively low frequency range.
The central portion of the intermediate layer may be constituted by a medium having acoustic impedance substantially equal to that of anyone of the piezoelectric layer, and the end portion of the intermediate layer is constituted by a medium having acoustic impedance substantially equal to or less than that of anyone of the piezoelectric layer.